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1/5 PetroCem Conference St. Petersburg, 2002
Dry Changes – Switch to Dry Processby Matthias Mersmann, KHD Humboldt Wedag AG, Germany
PetroCem Conference 200215.4.2002, St. Petersburg, Russia
AbstractEspecially thanks to the increased demand forcapital goods and to the realisation of infra-structural measures in the recent years, theforecast for the coming years sees a growthrate in the cement production in Russia. In amarket situation like this, it is not always easyto find the right balance between satisfyingmarket demands and overrunning investmentpossibilities. Modification of kiln plants, ratherthan building new ones, is the more realisticway to match sales opportunities to investmentlimitations. The robust machinery utilised in thecement industry allows to keep olderequipment in use, even within modified plantsforming new process technology.
This paper examines two realistic solutions tomeet the requirements for a modernisation ofwet process clinker production lines, which aretypical for Russia. Whether a regular dryprocess is to be favoured against a semi-dryprocess, depends on a variety of parametersand side conditions. Consequently, each andevery modernisation-project is a highly specificmatter, requiring individual treatment. Solutions“from the shelf” will most probably not lead tosatisfying results. A stepwise approach toincreased production and plant availabilitylevels out investment and pay back.
Apart from delivering complete new plants,KHD Humboldt Wedag has a long standingtradition in delivering tailor-made engineeringsolutions for the more effective utilisation andthe increase in efficiency of existing cementequipment. Based on the actual necessities ofthe cement producers, these solutions havealready proven their success in numerousinstallations world-wide.
KHD Humboldt Wedag AGKHD Humboldt Wedag is a world wide supplierof process know-how and machinery for thecement industry. Especially in Russia and the
CIS-states, we have a strong history throughour subsidiary ZAB in Dessau, the former East-Germany.
For more than 140 years KHD HumboldtWedag has been delivering key equipment andmachinery to the minerals and especially to thecement industry. For many of those machineswe hold first time and key patents, asHumboldt Wedag has and outstanding recordas a innovator for the cement industry.
An increasingly important task for us as aproprietor of cement process know-how, is theoptimization of the total production process bymeans of versatile and effective automationand expert systems.
Plant modification
General aspects and targets
picture 1 shows only the main aspects relatedto plant modernisation. Apart from the basiccondition of the plant, which has always to beconsidered, several other aspects like fuelsubstitution, reduction of production costs,production increase and environmentalaspects need to be taken into account. As canbe easily understood, there are manyinterdependencies among these and possibleothers.
Depending on where the focus of the projectshould be laid, the reasonable solution willstress the relevant fields without neglecting theside-aspects in order to optimize investmentcosts and functionality. However, a lot ofexperience is required to overlook all theimplications that come with bigger plantretrofits. Close cooperation betweenequipment supplier and cement producer arerecommended even at early stages in order toachieve essential project success.
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picture 1:Aspects and targets of plantmodification
Situation in Russia and the CIS States
picture 2 shows the multiple parametersituation specifically for the Russian cementindustry or the plants of the CIS states. Themajority of the installed pyro process lines inthis region of the world are wet process lines.The unavoidable high heat consumption aswell as the inherent low production capacity ofthis process now falls back on the cementproducers of Russia, that try to gear up fortheir future. Besides target production increaseand fuel costs, especially in Russia the chalkcontent of the raw materials is a decisive inputinformation. Maximum equipment re-use willbe mandatory to reduce investment costs in asurrounding of yet high uncertainty in futuremarket positioning. Kind and capacity ofstorage and conveying facilities will beinfluencing this field as well as process-typeand capacity of grinding equipment. In aspecific case, there will surely be even someother aspects in this multi-parameter decision.The careful evaluation reflecting theexperience from supplier and client as well, willdetermine the type of process to be installed inthe modification project.
In this example, the target production increaseand the fuel costs are rather high, whereas thechalk content within the raw material isrelatively low. The structural condition of theplant shall be in a bad shape, so that securingfunctional availability outweighs the need forequipment re-use. Especially the raw materialgrinding facilities are of very low capacity,which will favor a new raw mill. Although theconveying equipment consists of pipes and thestorage facilities are slurry tanks, theevaluation will lead in this case to a dryprocess plant.
picture 2: Set of parameters leading to adecision in favour of a dry process
The conversion to dry process would resultbasically in a shortening of the kiln, aninstallation of a cyclone preheater and thereplacement, or the adaptation of at least theinlet part of the clinker cooler. Of course, therespective drives must be checked forsuitability as well as the surroundingequipment.
picture 3 illustrates another situation. Givenonly slightly different preconditions regardingproduction increase, fuel costs and chalkcontent within the raw material, this case mightlead to another solution. As the plant in thiscase, is supposed to be in a good structuralcondition, and the grinding capacity of the wetgrinding compartment is sufficiently high, themajority of the equipment should be re-used.This way, the existing storage and conveyingfacilities will be incorporated into a semi-dryprocess.
picture 3: multiple parameter situationleading to a decision in favour of a semi-dryplant
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In contrast to the dry process, with the semi-dry process, a considerable amount of waterenters into the pyro-system through the “kiln-feed” (see picture 6). The most economic wayto pre-dry a slurry is to produce a filter cakewith a disk filter press. This filter cake is thenfed into the pyro-system. For that reason, afterthe shortening of the kiln, the preheater to beinstalled might only feature 3 stages. Thenumber of stages of the preheater conforms tothe water content of the filter cake. Theexhaust gas from the topmost stage is then ledinto a hammer crusher, in which also the filtercake is inserted. After breaking up of theagglomerates in the hammer crusher, theladen gas/cake-suspension is transportedupwards through the flash dryer, at the top ofwhich a twin cyclone serves for separating theparticulate matter from gas flow. The moisturecontent of the filter cake is now below 1 %.Finally, the down comer pipe will be connectedto the ID-fan to carry away the steam loadedexhaust gas.
The length of the rotary kilnAs can be seen clearly seen, shortening of theexisting rotary kiln will always be part of theprocedure. The following pictures (picture 4,picture 5)will illustrate, where this necessitycomes from.
picture 4: chemical and physical processesof the production of cement clinker in along rotary kiln
picture 4 shows the course of the chemicalreactions of cement clinker production in a longkiln. As the temperature follows the red line inthe course of time, different physical andchemical processes take place and variouscomponents and intermediate products aregenerated. The eye of the observerautomatically falls on the big triangle in light
blue representing Calcium Carbonate, which isto be converted into free lime by driving out theCarbon Dioxide. Along with drying andpreheating, this is not only the visually biggestpart of the process in this diagram, it actually isalso the most energy consuming part of theproduction process. Only the technicallyunavoidable heat losses contribute furthermoreto the energy consumption, because thesintering reactions themselves are in factexothermic, i.e. that energy is actually set freein the sintering zone. The total retention time ina long kiln process will be at least 1 hour.
In contrast to that, picture 5 shows theprecalciner process. When Humboldt Wedaginvented the 2-pier kiln technology in the1970’s, we asked for the major step in benefit,and we found out, that the drying, preheatingand precalcination (driving out of the CarbonDioxide) can better be done in a flowing gassuspension instead of a tumbling material layerin a rotary kiln. As we had invented the cyclonepreheater and the PYROCLON precalcinertechnology some years before, we knewexactly the potential of the Humboldt preheatercyclones and the PYROCLON precalciner.
picture 5: chemical and physical processesof the production of cement clinker in aprecalcination kiln
The increased efficiency of preheating andprecalcining not only leads to substantial heatsavings, but also to an intermediate product(“hot meal”), which is precalcined to up to 98%.This meal is ready to be sintered in the rotarykiln. As a consequence, it should betransported into the sintering zone as quicklyas possible, in order to obtain a controlled kilnprocess and avoid unfavorable ring coatings inthe kiln. For that reason, a regularlength/diameter ratio of these kilns is typically
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around 14/1, in some cases even down to11:1.
The reliability of this technical concept,consisting of cyclone preheater, maximumprecalcination and short kiln technology, hasmeanwhile been proven by KHD HumboldtWedag in more than 25 plants worldwide, aswell as the superior quality of the cementclinker produced with it.
Different ways to shorten a rotary kiln
If there is sufficient place alongside the existingkiln line, the favorable solution to build a newkiln might be beside the old one. We wouldcheck the existing kiln shell and the kilnsstructural features for possible re-use withinthe new system. During operation, the newtower structure, carrying the preheater (andeventually the precalciner) will be build besidesthe kiln. The new cooler and the foundationsfor the new kiln will be build. In a relativelyshort downtime, the selected section of theexisting kiln will be cut and erected again in itsnew position. Finally, the clinker transport willbe extended to fit to the new position.
The advantages of this strategy are of course:
• minimum downtime
• maximum possible re-use of parts (whichis, of course depending on the specificcase)
If there is not sufficient space availablealongside the kiln, the new kiln can also bebuild at the position of the old one, againkeeping as many of existing parts as possible.The screening of the kiln will check shellbending and inner shell stress, as well as loadcapacities of the roller stations. Duringoperation, the new tower structure, carryingthe preheater (and eventually the precalciner)will be build above the kiln. In the followingshut-down period, the kiln will be cut and thenew cooler will be installed. The existingtransport belts will preferably be re-used.
The advantages of this procedure are mainly:
• the minimum space requirements and
• the maximum possible re-use of existingparts
In some cases, when there is enough spaceavailable alongside the line, the cooler mightbe pre-erected and put into place at evenshorter downtime periods.
The Yingde plant, China as a typicalexample for Russian demandThe objective for the Yingde plant wascharacterized:
• by an increased demand of cement
• by the operation of 2 wet kiln lines with:
• low production
• low availability and
• high energy consumption
• The raw material contained a high amountof chalk
The client chose to install a new kiln plant ofsemi dry technology, what enabled him to keephis existing wet grinding and pre-processingequipment.
picture 6 shows the semi-dry pyro process lineof the Yingde cement plant. The major portionof the water contained in the slurry material ismechanically pressed out in a disk filter press.The product is taken as filter cakes, containingapproximately 20 % water, and is fed into thepyro system over a special rotary air lock. Thecakes fall into the hammer mill and are sweptout of it by the air flow into the flash dryer. Atthe top of the tower, the cyclone separatortakes out the particulate matter, which has nowbeen dried to a water residue of approximately1 %. A water spray system and a bypass lineare installed to control the dryer operationunder upset and start-up conditions. Apressure screw conveyor is used to feed thematerial in the consecutive 3 staged Cyclonepreheater. The PYROJET® kiln burnerintroduces only 45 % of the total fuel demandinto the kiln, the residual 55 % are fired in theprecalcination burner. Hot recuperated air istaken from the PYROSTEP® cooler and routedthrough the tertiary air duct to theprecalcination burner to serve as combustionair.
The process flow sheet in picture 6 showstypical data for the production of 1700 tons ofclinker per day. The disk filters are extracting110 t/h dry matter from the slurry. The moistureof these filter cakes that are fed into thehammer crusher/flash dryer unit is approx. 20%. The exhaust gas from the 3 stagedpreheater enters into the hammer crusher witha temperature of 535 °C to provide sufficientdrying capacity for the flash dryer, so that thetwin separator on top of the tower can take outalmost dry particulates, with a water content ofbelow 1 %. The overall pressure loss of thepreheater incl. hammercrusher, flash dryer and
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separator is slightly above 80 mbar. Theresidual equipment of the production linerepresents standard technology for a moderndry pyro process. The overall heatconsumption of this unit is below 3560 kJ/kgcli.
picture 6: process flow-sheet of a typicalsemi-dry process line
picture 7 shows the tower structure with itsvarious pipeworks. The central piece ofequipment for this process, the flash dryeritself, is the smallest of the three pipes in thecenter of this picture. The left pipe is theexhaust gas pipe of the 3 staged preheater,the extreme right pipe is the exhaust pipe ofthe separators that is routed towards the IDfan.
picture 7: tower structure of the Yingdecement plant, containing the flash dryer,the preheater and the precalciner
The performance parameters of the plantshow, that the switch to semi-dry has beensuccessful for this client, as specificconsumption of heat and electrical energy
have been remarkably reduced. Meanwhile,the client is installing a second identical lineparallel to this first one, which will becommissioned next year.
ConclusionOn the long run, many wet kiln lines in Russiawill be set out of operation. Dry processtechnology will be introduced into Russia andthe CIS states because of their higherefficiency in production as well as in heatconsumption . A lot of wet process plants willbe converted to dry process instead of beingbuild as new dry process plants. Plantmodernization, however, is a complextechnical procedure, that creates lots ofquestions and uncertainties for the cementproducer. To meet the requirements ofRussia’s cement industry of today, highlyeffective plant components embedded into asensible approach are needed. Re-use ofexisting equipment should be considered aswell as target efficiency benefit. In fruitfulcooperation with our clients KHD HumboldtWedag has successfully completed more than50 major plant modernizations in the last 25years.
Dry Changes - Switch to Dry Process (PetroCem Conference 2002) © KHD Humboldt Wedag AG, D-51170 Cologne, Germany
KHD Humboldt Wedag AG, Germany Phone +49-221-6504-1330, Fax +49-221-6504-1209, website: www.humboldt-wedag.de, email: [email protected]
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